This study is a randomized, double-blind, placebo-controlled, multicenter, parallel group comparison study designed to evaluate the efficacy of chronic, passive antibody immunotherapy employing one of two doses of a mucoid exopolysaccharide pseudomonas aeruginosa immune globin, intravenous (human) (MEP IGIV) in cystic fibrosis (CF) patients with endobronchial colonization by mucoid pseudomonas aeruginosa. MEP IGIV is selectively enriched for antibodies to the mucoid exopolysaccharide of P.aeruginosa (MEP) which support opsonophagocytic killing of the bacterium.